An automotive vehicle comprises one or more heat exchangers for cooling fluids used in the vehicle systems, such as refrigerant for an air conditioning system or transmission oil for a transmission device. A common heat exchanger comprises a plurality of parallel tubes connected at each end to a manifold and spaced apart by corrugated fins. Typically the tubes are formed of extruded aluminum. The manifolds include an inlet for receiving the fluid to be cooled and an outlet for supplying cooled fluid to other components in the system. The fluid enters the manifold through the inlet and is distributed to flow through passages within the tubes. Heat is extracted by air that flows through spaces between the corrugated fins between the tubes. The manifolds may include baffles that divide the manifold into sections and route the fluid back and forth in multiple passes.
It is known to manufacture a heat exchanger that is divided into separate sections for cooling different fluids. For example, heat exchangers are available that include a condenser section for cooling refrigerant and an oil cooler section for cooling transmission oil. The manifolds are divided by baffles to segregate the fluids. To facilitate manufacture, the tubes for both sections have the same outer dimensions. Because of the relatively high pressure of the refrigerant within the condenser section, the tubes include multiple internal webs to strengthen the outer walls and prevent distortion. The webs divide the cross section of the tubes into discrete regions of relatively small area. Because the refrigerant enters the heat exchanger as a gas, such small regions are effective in cooling and condensing the refrigerant. On the other hand, the transmission oil flowing through the oil cooler section is a liquid having a relatively low pressure and a relatively high viscosity. Small cross sectional paths, such as found in condenser tubes, result in a relatively high pressure drop for the oil. However, elimination of the webs to increase the size of the flow paths reduces contact between the oil and the tubes. This reduces cooling efficiency and necessitates an increase in either the length or number of tubes to achieve the desired temperature drop.
Therefore, a need exists for the heat exchanger having an oil cooler section that includes tubes extending between manifolds and sized and shaped to enhance the cooling efficiency for oil flowing therethrough, thereby reducing the length or number of tubes, and thus the size of the heat exchanger.